Damper operated switches for automatic heat control of gas fired unit ventilator



May 3, 1960 H. 6. SMITH 2,935,261

DAMPER OPERATED SWITCHES FOR AUTOMATIC HEAT CONTROL OF GAS FIRED UNIT VENTILATOR Filed Sept. 12, 1956 SOLENOID VALVE l I l LNVENTUR HERBERT G. SMITH ATTORNEY nited States Fatent DAMPER OPERATED SWITCHES FOR AUTOMATlC lfi%gRCONTRL 0F GAS FIRED UNIT VENTI- Herbert G. Smith, Moline, Ill., assignor to American Air Filter Company, Inc., Molina, 111., a corporation of Delaware Application September 12, 1956, Serial No. 609,412

2 Claims. (Cl. 236-1) Gas fired ventilators conventionally comprise: a cabinet having one air inlet for outside air, another air inlet for room air and an outlet for discharging air from either or both inlets into the room; a blower within the cabinet between said inlets and said outlet; 2. gas burning heater with the cabinet between the air inlets and said outlet; a damper for progressively opening and closing the outside air inlet between minimum and maximum positions; a reversible motor operable in one direction to open the damper and in the opposite direction to close it; and control means normally set for a predetermined room temperature condition and normally operative in response to a room temperature condition which rises above or falls below said predetermined temperature condition, to operate the motor progressively in the damper opening or closing direction as required.

With the room temperature at a desired value and with the damper wide open, the gas fiow to the heating element should be at a minimum or entirely cut off. However, as the room temperature drops and the damper progressively closes, the gas flow should be progressively increased. Various controls have been proposed to accomplish this control of the gas flow.

The principal object of the present invention is to provide a simple and inexpensive control for the heat output of the gas heater, one that will increase the gas flow in progressive steps as the damper progressively closes and decrease it in progressive steps as the damper progrossively opens.

In accordance with my invention, the principal object may be achieved simply and inexpensively, by providing the gas fired heater with a plurality of burners, each connected to the gas source through a separately electrically actuated valve energized by a respective switch, and by connecting the plurality of switches to the damper operating means in such a manner as to cause such means to open and close the switches in steps to decrease or increase the heat output of the heater progressively as the damper operating means opens or closes the damper.

The present invention is illustrated in the accompanying drawings wherein:

Fig. l is a diagrammatic view showing the electrical and mechanical relation between the operating elements forming the invention;

Fig. 2 is a vertical section taken through the unit ventilator and an adjacent building wall; and

Figure 3 is a schematic circuit diagram of the circuit elements forming the Wheatstone bridge.

The structure illustrated in the drawing conventionally comprises: an outside building wall 1, having an air inlet opening 2; and a room ventilating unit 3 having a blower 4 operated by a motor 5 for drawing air from its air inlet chamber 6 through an air filter 7 and a blower intake so as to discharge that air into the room through air outlet 9. The inlet chamber 6 of the ventilating unit 3 contains a damper 10 mounted for movement by a damper operating motor 11 from one extreme damper closed position to another extreme damper open position,

i.e., the dotted line position illustrated within Fig. 2. A gas fired heater 12 is mounted in the cabinet 3 between the blower 4 and the outlet 9. With the damper 10 closed, the blower 4 operates to recirculate room air successively through the inlet chamber 6, the air filter 7 and the heater 12, and to discharge that air through outlet 9 into the room. With the damper fully open, the blower 4 operates to draw only outside air through the outside inlet opening 2. When the damper 10 is in an intermediate position, the blower 4 will draw both room air and outside air in quantities depending upon the position the damper occupies relatively to the outside air inlet and the recirculating room air inlet.

The damper 10 is connected by a suitable linkage to a shaft 13 of the reversible damper operating motor 11 which is energized by a suitable control system.

The control system preferably is of the character described and illustrated in the copending application of Forrest G. Baker, Serial No. 426,770, now U.S. Pat. No. 2,843,324. This system (Fig. 1) may be energized from a suitable electrical energy source and includes a Wheatstone bridge 20 having temperature responsive resistances and a variable resistance controlled by the movement of the damper operating motor 11. The bridge 20, when energized, operates, in response to varying room temperature conditions, to feed varying currents to an amplifier 21 controlling the flow of current through a relay 22. When the control system is in a balanced condition, the bridge 20 causes the amplifier to feed an intermediate current to the relay 22 which balances the mechanical pull of a spring against the magnetic pull of a 'coil, energized by the intermediate current, to maintain the damper motor 11 de-energized. As the room temperature drops, the current to relay 22 decreases whereby the mechanical pull of the spring overcomes the magnetic pull of the coil to energize the damper closing circuit of motor 11 causing it to move the damper 10 in the damper closing direction until the control system is again in balance. Conversely, when the temperature rises, the current to the relay 22 increases and the damper opening circuit of motor 11 is energized causing it to move the damper 10 in the damper opening direction until the system is in balance.

The heater 12 includes a plurality of burners'23, 23', 23", connected by corresponding conduits containing respective electrically operated solenoid valves 24, 24', 24 to a header 25, which in turn is connected to a suitable source of gas supply. The solenoid valves 24, 24, 24"

are closed when de-energized and opened when energized.

A disc 26 is keyed to the shaft 13 of the damper operating motor 11 and carries a plurality of mercury switches 27, 27', 27", each mounted concentrically in a separate spaced sector of the disc 26 so that as the shaft 13 rotates, each switch will be closed or opened in succession as it moves through a predetermined angle with respect to horizontal. Normally, this predetermined angle will be the same for all the switches. For-example, assuming that shaft 13 moves between the extreme damper open and damper closed positions, the switches would be arranged about disc 26 so that all of them would be open in extreme damper open position and closed in extreme damper closed position.

One terminal of each of the switches 27', 27', 27" is commonly Wired to one side of a suitable source of electrical energy and the opposite terminal of each is wired to a terminal of one of the corresponding valves 23, 23, 23". The opposite terminals of the valves are commonly wired to the opposite side of the source of electrical energy. Figure 3 illustrates the essentials of the circuit elements included in a suitable Wheatstone bridge represented by the box 20 of Figure 1. As indicated earlier, Baker U.S. Patent 2,843,324 discloses the illustrated 3. structure and explains the operation thereof. In general, the Wheatstone bridge 26 is provided with a pair of power receiving terminals 31 and 31 and a pair of energy delivering terminals 32 and 33. The power receiving terminals 30 and 31 are connected to a suitable power supply. Theenergy delivering terminals 32' and 33 are suitably connected to the amplifier 21 as illustrated in Operation Assuming the damper to be in extreme damper open position, all the. valves 24, 24', 24. will be closed. The room temperature falls and the control system energizes the motor 11 to, start moving the damper 10 progressively in the damper closing direction. The movement of the motor 11 will continue until either the control system is balanced by the room temperature which deenergizes the motor or the damper is completely closed and all of the switches 27, 27', 27" are closed energizing all of the valves 24, 24, 24 causing them to open and admit gas to the burners 23, 23', 23". At'this time, the heater 12 will be operating at its maximum heat output and the blower 4 will be drawing all of its air through the recirculating room air inlet. During the movement of'the motor 11 in damper closing direction, the switch 27 will be closed after the shaft 13 has moved a predetermined amount, then switch 27' will be closed after theshaft 13 has passed through a larger predetermined amount of movement and finally the switch 27" will be closed after the shaft 13 has moved a still larger predetermined amount. In other words, the switches 27, 27', 27 will be closed in successive steps in that order during the movement of the shaft 13 in damper closing direction.

Next, assuming that the damper 10 is in extreme damper closed position and the room temperature is rising, the damper operating motor 11 will be energized to move the damperll) in damper opening direction. As this movement continues, assuming the rise in temperature condition continues to exist, the switches 27, 27', 27 will be opened in successive steps in that order to progressively reduce the heat output of the heater 12.

The movement of the damper 10 in either opening or closing directions and the corresponding opening or closing of the switches 27, 27 27" will continue until either the damper is in one of its extreme positions or the room temperature balances the control system causing relay 22 to de-energize the motor 11.

An exampleof how this system could be adjusted to perform is given in the table below:

Although an embodiment of the invention employing mercury switches appears to be preferable, applicant contemplates another embodiment in which the mercury switches are replaced by a series of push button switches operated by a cam driven by the motor 11.

Furthermore, the switches can be used to individually control two ormore valves and burners. In addition, instead of providing a single solenoid valve for each 1 burner, a plural stage valve could be'used to feed gas tion closing said outside air inlet and fully opening said recirculating air inlet and. a second limiting position fully opening said outside air inlet and closing said recirculating air inlet, a rotatable shaft for displacing said damper and means responsive to a departure of room tempera- 'ture. from a predetermined desired value thereof for selectively. displacing said rotatable shaft and pivotally mounted damper intermediate said first and second limiting positions in accordance wtih the direction of said departure from said desiredtemperature value to reduce the same, the improvement comprising a plurality of burners in said heater, an electrically operable valve for each of. said burners to control the admission of gas thereto, a switch for controlling, the energization of each of said electrically operable valves and means selectively responsive to the positional disposition of said damper displacing shaft for operating each of said switches in successive predetermined steps in accordance with the position of said damper relative to said outlet air inlet to maintain a predetermined inverse relationship between the amounts of air introduced through said outside air inlet and the number of burners in ignited condition whereby each of said valves is successively opened to admit gas to its respective burner in response to progressive displacement of said damper closing said outside air inlet and each of said valves is successively closed to decrease the heat output of said heater during reverse displacement of said damper. V

2. The improvement as specified in claim 1 wherein said switches are mercury switches arranged in circular array around a rotatably displaceable damper operating shaft and are rotatably displaceable in conjunction therewith.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Control Manual for Heating Ventilating andjAir Conditioning, copyright 1940 by the Minneapolis-Honeywell Reg. C0,, pages 149 and 153.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION May 3 1960 Patent No 2 935 26l Herbert G, Smith It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

for "with" read within line 35 Column l line 20 for gas flow" read gas flows column 4, line 36 for "outlet" read outside Signed and sealed this 10th day of January 1961.a

(SEAL) Attest:

KARL H, AXLINE ROBERT c. WAT-soN Commissioner of Patents Attesting Oficer 

